我有一个带侧栏的主窗口，用于导航和一个用户控件，在其中显示3个视图（默认，view1，view2）。在主视图模型（称为AppVM）中，我将contentcontrol初始化为默认视图，该默认视图具有一个按钮以前进到view1（除了导航侧边栏）。我在AppVM中有命令可以切换到三个视图中的任何一个。然后，View1有另一个按钮，该按钮应移至view2（使用主视图模型中存在的命令）。但是，每当我按下view1中的按钮（移至view2）时，显示都不会改变。特有的是，在调试时，在按view1中的按钮时，将内容控件绑定到的变量设置为Default视图，而不是当前视图view1。
[我认为我设置命令的方式会创建内容控件绑定变量的新实例，但我无法弄清楚如何使其使用同一实例，而不会一次又一次地打开新实例。
主视图模型（AppVM）
public class AppVM : ObservableObject
{
//Create a property that controls current view
private object _currentView;
public object CurrentView
{
get { return _currentView; }
private set
{
OnPropertyChanged(ref _currentView, value);
}
}
private string _textboxText;
public string TextboxText
{
get { return _textboxText; }
set
{
OnPropertyChanged(ref _textboxText, value);
}
}
//Instantiate the relaycommands, we will need to instantiate relaycommand objects for every command we need to perform.
//This means that we will need to do this for preses of all buttons
public RelayCommand View1ButtonCommand { get; private set; }
public RelayCommand View2ButtonCommand { get; private set; }
public RelayCommand DefaultCommand { get; private set; }
public AppVM()
{
//CurrentView = this;
CurrentView = new DefaultVM();
View1ButtonCommand = new RelayCommand(ShowView1, AlwaysTrueCommand);
View2ButtonCommand = new RelayCommand(ShowView2, AlwaysTrueCommand);
DefaultCommand = new RelayCommand(ShowDefault, AlwaysTrueCommand);
}
public void ShowDefault(object dummy)
{
// CurrentView = null;
CurrentView = new DefaultVM();
}
public void ShowView1(object dummy)
{
//CurrentView = null;
CurrentView = new View1(dummy as string);
}
public void ShowView2(object dummy)
{
// CurrentView = null;
CurrentView = new View2();
}
public bool AlwaysTrueCommand(object dummy)
{
return true;
}
}
View1 VM
public class View1VM : ObservableObject {
public InfoClass View1InfoClass { get; set; }
public View1VM() { View1InfoClass = new InfoClass //Apparently I need to instantiate and initialize this to activate binding {
FirstName = "Abbas",
//FirstName = passedInforClass,
LastName = "Syed",
Number = 12
};
} }
view1.xaml中的命令
<UserControl.Resources>
<vm:AppVM x:Name="AppVMinView1" x:Key="AppVMinView1"></vm:AppVM>
</UserControl.Resources>
<UserControl.DataContext>
<vm:View1VM></vm:View1VM>
</UserControl.DataContext>
<Grid Background="Aqua">
<StackPanel Margin="100">
<TextBlock Text="First Name"/>
<TextBox x:Name="firstNameTextBoxView1" Text="{Binding View1InfoClass.FirstName, Mode=OneWayToSource, UpdateSourceTrigger=PropertyChanged}"></TextBox>
<TextBlock Text="Last Name"/>
<TextBox x:Name="lastNameTextBoxView1" Text="{Binding View1InfoClass.LastName, Mode=OneWayToSource, UpdateSourceTrigger=PropertyChanged}"></TextBox>
<TextBlock Text="Random Useless Number" ></TextBlock>
<TextBox x:Name="randomUselessNumberView1" Text="{Binding View1InfoClass.Number, Mode=OneWayToSource, UpdateSourceTrigger=PropertyChanged}"></TextBox>
<TextBlock Text="First Name Entered"></TextBlock>
<TextBlock Text="{Binding View1InfoClass.FirstName}"></TextBlock>
<TextBlock Text="Last Name Entered" ></TextBlock>
<TextBlock Text="{Binding View1InfoClass.LastName}"></TextBlock>
<TextBlock Text="Random Useless Number Entered"></TextBlock>
<TextBlock Text="{Binding View1InfoClass.Number}"></TextBlock>
<Button DataContext="{DynamicResource AppVMinView1}" Content="Go to view2" Height="20" Width="70" Command="{Binding View2ButtonCommand}" />
</StackPanel>
</Grid>
[从我阅读的内容（在这里和在互联网上），我需要使视图成为单例，我尝试这样做的方式是为view2声明一个静态属性，并使用私有设置器将其初始化为新的view2。没有削减。我对此表示感谢。
我还应该补充一点，即使将view1中的按钮更改为view2也不起作用，侧面导航栏按钮也可以正常工作。
似乎您正在创建AppVm的多个实例。View1中的按钮和导航栏的按钮显然不会绑定到AppVm的相同实例。同样适用于CurrentView属性：与您在CurrentView中修改的View1相比，您的内容主机绑定到其他实例，即不同的属性值引用。因此，从CurrentView内部更改View1对内容宿主没有影响->视图永不更改。确保始终在相同的上下文中引用相同（共享）的实例。
根据用户界面的结构，有多种实现方法。到目前为止，创建视图模型类的Singleton是最糟糕的选择。应该并且总是应该避免单例。
最简单的解决方案是将视图模型声明为App中的资源，xaml ResourceDictionary：
App.xaml通过StaticResource标记扩展资源字典查找，可以在任何XAML上下文中全局使用此文件中定义的资源。
<Application>
<Application.Resources>
<AppVM x:Key="AppVMinView1" />
</Application.Resources>
</Application>
在任何XAML文件中（应用程序范围）：
<UserControl>
<UserControl.DataContext>
<View1VM />
</UserControl.DataContext>
<!-- Reference resources defined in App.xaml, using the StaticResource markup extension -->
<Button Command="{Binding Source={StaticResource AppVMinView1}, Path=View2ButtonCommand}" />
</UserControl>
看起来还好像您在视图模型内创建视图或页面的实例（我假设new View1(dummy as string)创建了控件，因为视图模型被命名为View1VM）。相反，仅使用视图模型可以更优雅地解决您的问题。
如果您不想在切换视图时丢失状态（和数据），则使用页面视图模型的单个实例非常重要。 （不要将其与Singleton混淆，后者是一种设计模式，通过将单个实例分配给static属性来确保使用单个实例，从而确保globally。Singleton Pattern通常被认为是反模式。）
这是关于如何显示和导航页面的简短但完整的示例：
AppVM.cs
// Main view model
class AppVM : ObservableObject
{
// Create a property that controls current view
private ObservableObject _currentView;
public ObservableObject CurrentView
{
get => _currentView;
private set => OnPropertyChanged(ref _currentView, value);
}
private Dictionary<string, ObservableObject> Pages { get; set; }
public AppVM()
{
// Create and store the pages,
// so that the same instances can be reused.
// All pages must extend ObservableObject (or any other common base type).
this.Pages = new Dictionary<string, ObservableObject>()
{
{ nameof(DefaultVM), new DefaultVM() },
{ nameof(View1VM), new View1VM() },
{ nameof(View2VM), new View2VM() },
};
// Initialize first page
this.CurrentView = this.Pages[nameof(DefaultVM)];
this.DefaultCommand = new RelayCommand(param => this.CurrentView = this.Pages[nameof(DefaultVM)], param => true);
this.View1ButtonCommand = new RelayCommand(param => this.CurrentView = this.Pages[nameof(View1VM)], param => true);
this.View2ButtonCommand = new RelayCommand(param => this.CurrentView = this.Pages[nameof(View2VM)], param => true);
}
}
View1.xaml
<!-- DataContext is inherited from the surrounding DataTemplate and is the corresponding page view model -->
<UserControl>
<StackPanel>
<TextBox Text="{Binding View1InfoClass.FirstName}" />
<!--
Bind to the command of the same view model instance,
which is the DataContext of the content host
-->
<Button Content="Show View2"
Command="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType=MainWindow}, Path=DataContext.View2ButtonCommand}" />
</StackPanel>
</UserControl>
MainWindow.xaml
<Window>
<Window.DataContext>
<AppVM />
</Window.DataContext>
<Window.Resources>
<!-- Define the views as implicit (keyless) DataTemplate -->
<DataTemplate DataType="{x:Type DefaultVM}">
<DefaultView />
</DataTemplate>
<DataTemplate DataType="{x:Type View1VM}">
<View1 />
</DataTemplate>
<DataTemplate DataType="{x:Type View2VM}">
<View2 />
</DataTemplate>
</Window.Resources>
<!--
Host of the pages.
The implicit DataTemplates will apply automatically
and show the control that maps to the current CurrentView view model
-->
<ContentPresenter Content="{Binding CurrentView}" />
</Window>